<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button onclick="ajaxFun()">请求</button>
    <button onclick="alert('666')">弹框</button>
    <p></p>
</body>
<script>
    function ajaxFun(){
        let xmlHttp = new XMLHttpRequest()
        xmlHttp.onreadystatechange = function(){
            if(xmlHttp.readyState == 4 && xmlHttp.status == 200){
                let res = xmlHttp.responseText
                document.querySelector('p').innerHTML = res
            }
        }
        xmlHttp.open("get","http://127.0.0.1:3000/ajaxdemo",true)
        xmlHttp.send()
    }
</script>
</html>